A valve is a mechanical device, which opens and closes in order to control the flow of materials, such as water, stream, oil, and gas chemicals, in flow lines such as pipes and vessels. Valves are used in a wide variety of familiar devices and many known tasks. For example, turning a dial on a gas stove varies the opening of a valve and regulates the flow of gas to the stove burner. The valve in an automobile tire allows air to enter but not to leave the tire. Valves in a steam radiator permit the air in the radiator to leave and the steam to take the place of air. In addition, valves may vary in size from a fraction of an inch to several feet, depending upon the diameter of the pipe or passageway. Valves are joined to a pipeline by threaded, flanged, or welded joints.
Some conventional valves consist of two main sections that form the valve housing/body: the bonnet section and the body section. The features of a conventional valve also include inlet and outlet openings to enable materials to flow through into, through and out of the valve. The valve also includes a restriction component (often referred to as a plug) that can be positioned in the area between the inlet and outlet opening to partially or totally restrict the flow of materials through the valve and thereby affect the flow rate and pressure of the materials. The fourth feature of the valve comprises an actuation mechanism to control the positioning of the restriction component between the two openings. Valve operators usually adjust the position of the restriction component through the actuation mechanism.
Valves fall into two broad types: linear and rotary. In a linear valve, the disc/plug lifts from the seat and moves in a direction that is perpendicular to the seat. By comparison, in a rotary valve such as a ball valve the disc rotates in the seat. Shown in FIG. 1 is a traditional type of linear valve called a gate valve. This valve has a stem 10 and plug 11 that moves in an up and down linear directions. A wheel 12 connects to the stem 10. The operator rotates the wheel in one circular direction (usually clockwise) to lower the plug into the flowline 13. Rotating the wheel in the opposite circular direction will cause the stem to move upward and thereby raising the plug out of the flowline. The valve also contains a bonnet 14 and a body 15 that form the valve housing.
This gate valve is ordinarily used in industrial and power-plant piping systems when it is necessary for the valve to be either fully open or entirely closed. This type of value (fully opened or fully closed) is fundamentally known as a shutoff valve. When the valve is open, the fluid passes straight through the flowline 13, with little restriction to cause pressure loss. In the solid-wedge type of gate valve, the plug 11 is forced down into two seat rings set at a slight angle. In the split-wedge, or double-disc, valve, the plugs are forced against the seats (body 15) by the wedging action of the stem 10 as it is screwed down.
FIG. 2 illustrates a traditional globe valve. This valve is named for its shape. Similar to the gate valve, this globe valve comprises a wheel, stem, bonnet, plug and body. The main difference as shown is a different lower configuration of the bonnet 14 and the body 15. In addition, FIG. 2 shows a different configuration for the plug 11. This valve interposes greater resistance to flow than the gate valve and is not pressure balanced except where control of flow or pressure, called throttling is required. The globe valve is superior to the gate valve for throttling service. In addition, globe valves always have rising stems. The hand wheel turns the screw in the threads of the bonnet, thereby either raising or lowering the plug.
Another type of valve is the diaphragm valve. This valve is similar to the globe valve except that a diaphragm of flexible material is clamped between the body and the bonnet. The valve stem, regulating the size of the opening through which the fluid flows and shutting the valve off when pressed down onto the seat, moves up and down the diaphragm. This construction isolates the working mechanism of the valve from the fluid. It requires no repacking or reseating, and is designed for corrosive and abrasive fluids, or for fluids carrying solid particles in suspension.
FIG. 3 shows a traditional check valve used to prevent reversal of flow in a pipeline or flow line 25. A check valve is similar in function to an electrical diode. This valve allows free flow in one direction but prevents flow in the opposite direction. There are two principal types of check valve: the swing check and the lift check. The swing check has a flapper disc 20 connected to a hinge 21. The hinge 21 is connected to a check valve cap 22. Flow shown in the direction shown in FIG. 2 will cause the disc to the flapper disc to swing down and seal against the seat 23 of the body 24. Fluid pressure in the direction 26 on the disc forces the disc down against the seat 23 and seals off the fluid flow. If the fluid flow reverses, the fluid pressure would cause the disc to swing up, allowing free flow of the fluid in a predetermined direction. A lift check operates similarly except that the disc rises vertically in a cylindrical guide.
The regulating/control valve differs from the shutoff valve in that the regulating valve maintains a constant but restricted flow and pressure. Often, these valves automatically vary the opening through the valve, thereby varying the flow of liquid. This regulated flow maintains a prescribed pressure. Moving the valve stem and the valve disc with respect to the seat does this variance. In many valves, the disk is generally of a special shape to provide the desired regulating characteristics. In the simpler types of valves the pressure to be maintained is applied to a diaphragm attached to the valve stem. This pressure is opposed by a spring or weight; the pressure to be maintained is adjusted by changing the spring tension or moving the weight on a lever. The pressure on the diaphragm usually comes either from the upstream or downstream pressure, whichever the regulator is set to control. There is usually no external power or actuation applied to the valve.
With respect to rotary valves, the ball valve has a spherical ball with a horizontal bore. The ball fits between two vertical seats each sealing against the ball in different directions. The valve stem rotates the ball 90°. When open, the ball's bore is aligned with the body's bore allowing free flow of the fluid. When rotated to the closed position, the ball's bore is perpendicular to the body's bore and the seats seal tightly on the ball's surface.
The rotary control valve is similar to the regulating valve. A power actuator, usually pneumatic, actuates the control valve or electric, conforming to a signal sent to the valve from a controller. A controller is a device that measures fluid flow rate, temperature, or pressure and compares the measurement to a preset valve in the controller. The controller sends a signal to the valve telling the valve to open to a proper position such that the flow measurement matches the preset valve. Control valves can have either linear motion or rotary motion. Control valves are used in almost all fluid control systems. A control valve is seldom closed or fully open. The control valve throttles fluid flow by causing a drop in fluid pressure across the valve. This function requires the valve to have a high resistance to flow erosion. The pressure drop may also cause cavitation in liquid flows and noise in gas or stem flows. Special valves have been designed to resist cavitation and to reduce noise.
In addition to the conventional control valves, there are also inline control valves. However, unlike conventional valves, that have a restriction mechanism that comes into and out of the flow path, the inline control valves have a fixed diverter member or plug positioned centrally of the flow passage with the fluid passageway of the materials flowing through the valve. This diverter has a uniform cross sectional area generally equal to the cross sectional area of the upstream and downstream flow passages to provide equal flow about the diverter member. A sleeve of a generally cylindrical shape is normally provided as a closure member for sealing against the fixed diverter member. The sleeve moves in a longitudinal direction between open and closed positions relative to the fixed diverter member.
Inline control valves can have a diverter that is spring biased and is moved by the pressure of the material flowing through the valve. This flow pressure varies the position of the diverter and therefore the flow path and the flow rate of the materials flowing through the flow line. This concept is similar to the previously discussed regulating valve.
There are various types of inline control valve designs. For example, U.S. Pat. No. 2,416,787 shows an inline control valve in which a fixed plug is mounted centrally of the flow passage and has a sleeve movable between open and closed positions relates to the fixed plug. The sleeve is urged by a separate source of pressurized fluid into a closed position against the fixed plug.
U.S. Pat. No. 2,590,466 shows a multi-stage sleeve valve having a fixed diverter member with a pair of discs to provide a two-stage seating of the sleeve against the fixed diverter member. Pressurized fluid from a separate fluid source urges the valve into sealing engagement with the fixed diverter member.
U.S. Pat. No. 4,880,206 shows a magnetic control valve in which the sleeve is fixed and a movable inline valve member forms the closure member and moves between open and closed positions relative to a fixed annular seat. A magnetic coil surrounds the valve member and the valve member forms a magnetic armature so that upon energizing of the magnetic coil, the valve member moves to a closed position. The outer annular seat does not move and does not form a movable closure member.
U.S. Pat. No. 5,435,337 describes an inline control valve for controlling fluid flow in which a fixed plug or diverter member is positioned centrally of the flow passage and a passageway formed between the plug and the outer housing is such that the cross sectional area is identical along the entire passageway thereby to provide equal flow along the plug to minimize turbulence. A sleeve of a generally cylindrical shape forms the closure member and moves between open and closed positions relative to the fixed plug. The sleeve is responsive to fluid pressure within the flow passage and is normally urged into closed position by the fluid pressure.
Although, many inline control valves exist, the pressure of the materials flowing through the valve activates the current inline valves. Many of these valves are spring biased to regulate the flow of the material through the flowline.
Mokveld offers an axial flow control valve that claims to significantly reduce noise and turbulence and prevents the erosion of untreated fluids in upstream applications. Mokveld claims that the in-line and symmetrical flow path eliminates indirect flows and unnecessary changes in flow direction through the valve. This valve has a two-piece actuation mechanism, which comprises first and second perpendicular rods. The first rod is attached to a piston positioned in the flowline. Movement of the second rod in a linear direction causes the movement of the first rod and attached piston in a linear direction. Although this valve incorporates the concept of an in-line flow control valve with an external actuation mechanism, the complicated nature of this design makes it a less attractive alternative.
There remains a need for an inline control valve that can be activated from an external location. In addition, there remains a need for a control valve that has a one-piece design to facilitate more efficient maintenance of the control valve. A one-piece design would eliminate the need to separate and dissemble the two-part housing of a conventional control valve. As previously mentioned, most valve housing designs have two main parts. During any maintenance to the valve, there will be a need to separate the these parts. As a result, the typical approach is the simply replace the valve needing maintenance with a new valve and then perform maintenance of the valve offline.
There remains a need for a valve that is assembled such that it is not necessary to separate the upper and lower portions of the valve during assembly and or maintenance.